Abstract
Aim: The aim of the present study was to evaluate the resistance to cyclic fatigue of different nickel-titanium (NiTi) rotary instruments. The tested instruments were Protaper Gold (PTG), HyFlex EDM (HEDM) and K3XF.
Materials & Methods: A total of forty-five NiTi rotary instruments were divided into three experimental groups (n = 15 each). Group 1: Protaper Gold (F2 25/.08), group 2: HyFlex EDM (25/.08) file and group 3: K3XF file (25/.08). The testing device was specially designed for this experiment. The cycles to failure were calculated. The data were statistically analyzed using one-way analysis of variance (p < 0.05).
Results: The results revealed that HyFlex EDM showed statistically significant highest mean cyclic fatigue value, while K3XF showed statistically significant lower mean cyclic fatigue value. Protaper Gold system showed statistically significant lowest mean cyclic fatigue value.

Conclusions: The geometrical design features and mode of manufacturing of the tested nickel-titanium rotary systems have a direct influence on their resistance to cyclic fatigue. HyFlex EDM files demonstrated significantly higher cyclic fatigue resistance than Protaper Gold and K3XF. The electrical discharge machining (EDM) technology and the unique cross section of HyFlex EDM may be the main reason for this difference.